1. Field of the Invention
This invention relates to cryosurgical instruments, and more particularly to directly valved, cryosurgical instruments.
2. Description of the Prior Art
The first hand held cryosurgical instrument for general surgical use is set forth in my U.S. Pat. No. 3,534,739. That instrument controlled the venting of continuously, self-boiling cryogen in order to force the delivery of liquid cryogen as desired. Since the device is continuously vented, except against the pressure induced by the operator in manipulating the vent closing valve thereof, no pressure relief was necessary, and none of the liquid cryogen flowed through the valve. As clinical history developed in the years following the introduction of this hand held cryosurgical unit, more and more usage was found therefore.
In attempts to provide lower cost cryosurgical units which would utilize the liquid cryogen more economically by reducing the rate of boiling thereof while in the reservoir of a cyrosurgical instrument, standard, commercial vacuum bottles having dual metallic walls have been used as the basis for construction of cryosurgical instruments. These devices, it has been found, have numerous drawbacks. First of all, since the intent is to conserve nitrogen, the devices were not provided with normally open vents, the closing of which would force liquid through the delivery tube, but rather were provided with valves directly in the cryogen delivery tube, with pressure relief valves to avoid the buildup of excess pressure therein.
The provision of low cost valves capable of being used directly in the liquid cryogen delivery line has given rise to additional problems, such as freezing of the valve in either the open position or in the closed position, or both. No provision has heretofore been made to alleviate the freezing when it occurs, other than setting the instrument aside until it can thaw suitably from ambient temperature.
The cryosurgical instrument disclosed in my aforementioned patent utilizes a control valve which is symmetrically disposed with respect to the delivery tube, and is therefore equally useful for right-handed and left-handed surgeons. However, it is limited to operation by the thumb (or in some equivalent manner). Certain of the instruments which have been offered as low cost instruments are designed in a fashion which totally commits them to preferential use either by the right hand or the left hand. Thus, not only is a right-handed instrument likely to be unwieldly for a left-handed surgeon to use, interchange between the two hands of a surgeon as desired or between surgeons of different handedness is hampered by designs which are available in the art.